1. Field of the Invention
The present invention relates to electronic components, and, more particularly, to an electronic component including a filter.
2. Description of the Related Art
As a known electronic component in the related art, for example, a multilayer LC filter is disclosed in Japanese Unexamined Patent Application Publication No. 9-307389. FIG. 4 is a partially exploded perspective view of a laminate 102 in a multilayer LC filter 100 disclosed in Japanese Unexamined Patent Application Publication No. 9-307389. FIG. 5 is an equivalent circuit diagram of the multilayer LC filter 100.
The laminate 102 includes laminated rectangular insulating layers 104a to 104g, an inner conductor 105, and strip lines 106a to 106c. The inner conductor 105 is disposed on the insulating layer 104b, and functions as a shield to prevent an unnecessary wave from entering the laminate 102. The strip lines 106a and 106c are disposed on the insulating layer 104d, and extend along short sides of the insulating layer 104d. The strip line 106b is disposed on the insulating layer 104f, and extends between the strip lines 106a and 106c along short sides of the insulating layer 104f in plan view from a lamination direction. A capacitor layer is disposed under the laminate 102, and is connected to the strip lines 106a to 106c via an external relay electrode.
As illustrated in FIG. 5, the multilayer LC filter 100 includes three LC resonant circuits LC101 to LC103. The LC resonant circuit LC101 includes a coil L101 and a capacitor C101. The strip line 106a forms the coil L101. The LC resonant circuit LC102 includes a coil L102 and a capacitor C102. The strip line 106b forms the coil L102. The LC resonant circuit LC103 includes a coil L103 and a capacitor C103. The strip line 106c forms the coil L103. The LC resonant circuits LC101 and LC103 are connected to an input electrode 110a and an output electrode 110b via capacitors C100 and C104, respectively.
In the multilayer LC filter 100 having the above-described configuration, the strip lines 106a and 106b are electromagnetically coupled to each other, and the strip lines 106b and 106c are electromagnetically coupled to each other. As a result, the multilayer LC filter 100 forms a band-pass filter.
An exemplary operation of the multilayer LC filter 100 will be described. As illustrated in FIGS. 4 and 5, one end of the coil L101 (the strip line 106a) is connected to the input electrode 110a via the capacitor C100, and the other end of the coil L101 (the strip line 106a) is connected to the ground. Therefore, a current i101 passes through the coil L101 from the input electrode 110a to the ground.
The coil L102 is connected to the capacitor C102, and is not connected to the ground. The strip line 106a (the coil L101) and the strip line 106b (the coil L102) are electromagnetically coupled to each other. Accordingly, when the current i101 passes through the strip line 106a (the coil L101), a current i102 passes through the strip line 106b (the coil L102) in a direction opposite to that of the current i101 by electromagnetic induction as illustrated in FIG. 4.
As illustrated in FIGS. 4 and 5, one end of the coil L103 (the strip line 106c) is connected to the output electrode 110b via the capacitor C104, and the other end of the coil L103 (the strip line 106c) is connected to the ground. Therefore, a current i103 passes through the coil L103 from the output electrode 110b to the ground.
As will be described later, in the multilayer LC filter 100, it is difficult to achieve both miniaturization and the narrowing of a frequency band. More specifically, since the strip lines 106a to 106c forming the coils L101 to L103 are straight in the multilayer LC filter 100, magnetic fluxes are generated around the strip lines 106a to 106c. In this case, the magnetic fluxes generated at the coils L101 to L103 are distributed over a relatively wide area. Accordingly, the coils L101 to L103 are easily electromagnetically coupled to one another, and a coupling coefficient among the coils L101 to L103 is increased. When a coupling coefficient between coils is increased, a pass band for a signal is broadened. Accordingly, in the multilayer LC filter 100, a pass band for a signal is broadened.
In order to reduce the coupling coefficient among the coils L101 to L103, a method of increasing the distances between the strip lines 106a to 106c may be considered. Using this method, magnetic coupling among the coils L101 to L103 can be weakened.
However, in this case, the multilayer LC filter 100 is increased in size. Therefore, it is difficult to achieve both miniaturization and the narrowing of a frequency band in the multilayer LC filter 100.